This invention relates to a rotating surgical tool for removing thin layers of articular cartilage and bone from bone members in the preparation of a joint socket to receive a joint prosthesis.
In the treatment of severe cases of arthritis and other degenerative joint diseases, particularly of the hip joint, it is now common practice to shape the hip joint socket and remove the hip joint ball and to thereby be replaced by a total hip prosthesis formed from artificial materials. Prior to installing the artificial hip joint socket, articular cartilage and bone is removed from the socket in the process of reshaping the acetabulum to accurately match the dimensions of the artificial socket.
In the past, numerous types of milling devices and reamers have been employed with various degrees of success. Some of these devices are disclosed in U.S. Pat. No. 3,630,204 (Fishbein), U.S. Pat. No. 4,023,572 (Weigand et al.), U.S. Pat. No. 4,116,200 (Braun et al.) and U.S. Pat. No. 4,131,116 (Hedrick). Although the devices described in these patents represented substantial improvements over the crude devices which preceded them, i.e., rasps, hammers and chisels, the devices described therein cannot provide the accurate reshaped cavities and the smooth cavity lining required by the modern surgical prosthesis. Moreover, many of these prior devices were costly to manufacture and some could not be aseptically cleaned without the inconvenience of disassembling numerous component parts.
Preferably, the cutting edges of the surgical tool should be able to cut through a wide variety of tissue, such as joint cartilage and bone tissue, ranging in density from the porous or cancellous tissue to the hard sclerotic bone. Surgical tools which merely scrape or tear off tissue operate well on hard bone but they tend to be less effective with soft, porous tissue.
The surgical tools with hollow cutting heads are more widely used than other more open designs because with the hollow head devices cuttings and other debris are captured within the interior of the cutting head so they will not interfere with subsequent procedures. However, the hollow cutting heads are usually drawn into their hemispherical shapes and this method cannot form cutting heads with the accuracy frequently needed. Additionally, if the cutting surfaces are formed integrally with the shell such as with teeth or raised edges of slots, the manufacturing thereof becomes very costly. Resharpening of the cutting surfaces of these tools is for the most part impractical, so the entire cutting shell must be discarded when the cutting surfaces dull.
Ideally, a surgical device for shaping a joint socket such as the acetabulum should be simple in design and construction and economical to manufacture. At present, up to about 30 different sized cutting heads must be available with an incremental difference of 1/2 mm in the cutting radius between the various sized blades. In order to reduce the manufacturing cost of the devices, it is preferred to have as many standard components as possible. Generally, it is preferred to have a standard sized drive mechanism with the cutting heads of different sizes being adapted to fit on the single drive mechanism. The securing mechanism between the cutting heads and the drive mechanism should be as simple as possible to avoid complicated assembly in changing heads. Moreover, not only should the cutting heads of different sizes be readily changed but also cutting heads of different shapes such as frusto-conically shaped cutting heads should also fit on the same drive mechanism. The device of the present invention satisfies these requirements.